Artificial horizon



L.. F. l@ARTER ARTIFICIAL HORIZON Filed July 1, 1938 IKW/Imm Num 2 sheets-sheet i h NvQENToR Feb. 20, 1940. L. F. CARTER- 2,190,698

ARTIFICIAL HORIZON l Filed July 1, 1938 2 sheets-sheet '2 ?atented eb. 2G, i949 4uNrrEn STATES alertas i alcances ARTIFICIAL nomzoN Leslie F. Carter, Leonia, N. J., assignor to Sperry Gyroscope Company, Inc., BrooklynyN. Y., a corporation kof New -York Applieaion' July 12.1938, sei-m No. V216,95*:

s claims. (01. 'i4-si This invention relates to the art of artificial horizons, wherein the purpose is to maintain al reference plane as nearly `horizontal aspossible, regardless vof disturbing forces which may act upon the instrument. More particularly, the invention relates to improvements in artiiicial horias well as the viscosity of the damping medium.

zons or gyro-verticals used on'aircraft.

The common practice is to use gyroscopes with a vertical spin axis and supported in neutral ror even of only several minutes of arc will result f- 'in an appreciable error in the position calculated when using the gyroscopically maintained horizontal reference plane, so that extreme accuracy is required. L It is the purpose of this invention to overcome the inaccuracies and errors of the present gyrolscopic artiiicial horizon. It is commonly known that a vertical gyroscope is subject to a so-called i i flatitude error caused by the eilect of the earths vrotation upon the gyro. This error is proportion-` al to the cosine of the latitude and,- with present day high speed airplanes, such error would change quite appreciably in a relatively short time, so

that correction is difficult.

Another error is the speed error which is caused' by the effect of the speed of the craft, as

it adds orv subtracts from the circumferential speed of the earth. As modern airplanes may y .u i .at speeds upward of 300 miles per hour, it is ob-r vious that the speed error will also be large.

vThis invention combines a vertical gyro with a damped long period pendulum, wherein'I employ the pendulum instead of the gyroscope to 45 'furnish the 'horizontal reference plane, while the fgyro itself is used only for the purpose of' supporting the pendulum on a platform which is kept substantially horizontal, so that the 'rolling and pitching angular movements of the craft'do not so reachjthe pendulum. 'I'his combination will avoid the above mentioned latitude and speed errors because a pendulum is not subject to these errors, and slow changes of the position of the vertical axis of the horizon gyro lwill not be transv of air iets. Following the usual practice. the

mitten to the4 pendulum.

l centrifugal forces.

" Referring to the drawings,

In order to prevent the pendulum from oscil- 4latingat its own natural period, vIprefer to apply damping means between the lpendulum and the gyro casing, so that the damped period oi? the pendulum may be made of any desired value by Y 5 choosing the location of the center of gravity A further object of va modified form of my inf vention is to prevent the artiilcial horizon from assuming errors due to lateral acceleration forces 10 caused by a change of course of the craft. Normally, the pendulous erecting means of the gyro tend to gradually -precess the lgyro until it lines up with theapparent vertical, and so the pendulum itself is also directly deiiected. I prol5 pose to cut olil' the erecting devices and at the same time. to arrest the 'pendulum in such away that it becomes 'rigidly connected to the gyro case during therpresence of acceleration forces,

.due to tuming and the, like.' simmtaneously, a ,o v

weight is shifted in such a way as to compensate for the change 'in the position 4of the centerloi' gravity of y,the whole assembly, which otherwise would becomev pendulous as soon as the pendulum is rigidly connected to the gyro case. As the 95 initial ,balance of the gyroscope itself is made for neutral equilibrium, the above described pro'- cedureisnecessary in` order -to prevent spiral oscillations of .the gyro under the influence of` v Fig. 1 is avertical section of /a preferred form of my invention, taken along line l--I oiFlg. 2.

Fig. 2 is a horizontal section through the same instrument taken along line 2--2 of Fig. 1. 35 Fig 3 shows a vertical section through a. modifled form. of my invention, along line 3-3 ofv Fig. 4. 'Y

Fig. 4 is a horizontal sectionthrough the same instrument along line 4-4 of Fig. 3. o

Fig.l 5 shows a simple means for automatically 4 shutting off the air supply i'orthe erector and arresting the pendulum during turn of the craft.

In Figs. 1 and 2, the gyro rotor` is-shown-as a cup-'shaped member 5 having its shaft 6 mount' 45 ed in ball bearings in the casing'l. The casing I0. The casing is preferably mounted in neutral so equilibrium and is erected by gravitationally responsive means such as shown in the prior patent to Carlson #1,982,636, dated December 4, 1934.

The gyro rotor 5 is shown as spun by'means casing IU is evacuated through a pipe (not shown) so that the pressure inside of the housing ID is lower than that of the surrounding atmosphere. Air will enter through the iilter or screen I I, from there through passages around the bearing I2,

through the perforated pivot I3, and into an inner-air chamber III in the gimbal ring 9, by which it is conducted to the perforated pivots 8 and 8. Two jets I5 and I5' are supplied with air through passages I6 and I6 located within the wall of the casing lI. Due to the evacuation of the housing I0, air will stream out of the jets I and I 5 and drive the gyro rotor at high speed. y

Referring now to Fig. 1, the air, after it has driven the gyroscope, will escape through the passage I'I into the chamber I8, from where it emerges through ports I9 and I9. The opening of these ports is controlled in known manner by the auxiliary small erecting pendulurns 20 and 2li for one axis and 2i, 2I for the other axis. The action of these pendulums and jets is fully described in the above mentioned patent to B. G.

Carlson. l

The casing I carries at its upper rim a cup 22 which, in its lower part, is spherically shaped and which occupies most of the free space inside of the cup-shaped gyro rotor 5. A pendulum 23 having a spherically shaped body is mounted on a small gimbal system 25, 25 yon a member 2t supported on top of the cup-shaped member 22 and held to the gyro casing 'I by screws 2. A balancing weight 2B may be mounted on top of the member 2liA to obtain neutral, equilibrium of the whole assembly. The' narrow space be` tween the spherical part of the cup 22 and the spherical body of the pendulum 23 is preferably partly filled by a. viscous liquid, such as oil or the like, which serves as a damping medium. i

According to my invention,` I mount the reference member 301m the pendulum, instead of on the gyroscope, as has heretofore been the practice. A stem 29 is connected to the pendulum 23 and carries at its upper end thereference member, which in this case is a iiat, polished plate 30 which serves as a mirror and which may have engraved upon it reticle lines or other marks of l reference.

In operation, this combined gyro and pendulum will maintain the plate 3&3 in a horizontal plane with great accuracy, as the normal posi'- tion of the pendulum will be the true vertical as long as no lateral acceleration forces are present, and as roll and pitch motions of the vehicle are eliminated by the stabilizing action of the gyroscope. The cup member 22, which serves as the point from which the pendulum 23 is damped, is kept in a substantially horizontal position by the action of the gyroscope, and only subject. to the above explained errors common to all self-erecting vertical gyros. The pendulum 23, however, is free from the gyro errors, the changes of which only occur very slowly and therefore are not transmitted to the pendulum itself.

In case of turns of the vehicle on which the instrument is carried,v it is obvious that both the pendulum as well as the gyroscope will ultimately line themselves up4 with the apparent vertical,

and therefore indicate an erroneous reference plane. To overcome this, I have shown a modif fied artificial horizon in Figs. 3 and 4, which is automatically freed from the effects of centrifugal acceleration forces during turns by interconnecting the shut-olf valve with a turn indicator gyro, as will be described hereinafter. The ref- `the before described erection device.

erence numbers in Figs. 3 and 4 correspond to those in Figs. 1 and 2.

As will be seen in Fig. 4, the casing I is diier1 ently constructed than that shown in Fig. 2. The two jets I5 and I5 are supplied with air through a single passage 3| which is connected to the plate 39 is mounted xedly in the casing IIB and has a plurality of holes which, when the shutter is open, are in exact alignment with an equal number of holes in the rotatable plate 38, which can be turned by the knob t0. If the knob it is turned through an angular amount corresponding to the diameter of the ports 3l, no air will be allowed to enter.

The air from channel 3d and through pivot 33 enters into a passage dl, from where it is conducted into the chamber I3 in order to operate The passage I, through the channel lll', is also connected to the inside of an annular bellows 32 which, due to the difference of pressure between the outer atmosphere and the air inside of the bellows, is normally in an expanded condition. At the lower end of the bellows 33 there is attached a member 433 made out of a suitable resilient material which serves at least one, and preferably two purposes, namely, (l) temporarily to lock the gyro to the housing and (2) to compensate for the change of center of gravity'of the whole assembly after the pendulum has been so locked. For this purpose the stem 23 of the pendulum 23 has been provided with a circular conical collar d which fits a similar conical recess in the weight 53. If the air supply to the passages dl and III is interrupted by the shutter 38, the resilient bellows d2 will contract and lift the weight Q3 up until it seats itself upon the conical collar l5 of the stem 23, thereby arresting the pendulum. At the same time a predetermined amount of weight has been lifted a predetermined distance, which is so calculated that the product of weight and distance of the center of gravity of the weight from the gimbal center is equal to the product of the unbalanced weight of the pendulum 23 and the distance of its center of gravity from the same gimbal center.m In this way the equilibrium of the whole assembly is kept constant, so that acceleration forces cannot act upon the gyro itself.

At the same time'the shutter 38 also prevents further air jet eiect from the ports I5 and I5', so that there is no erecting force present to precess the gyro into the apparent vertical.

The air which has been used tospin the gyro rotor 5 escapes through passages t5' into a diffusion chamber d6 filled with porous material which will let the air pass through, but which will prevent the formingk of any jet effects at the ports 5l, d8, 53 or 53.

Fig. 5 shows schematically how the automatic operation of the shutter 33 is accomplished by means of a turn indicator gyro. 5l is the housing of a turn indicator gyro and shaft 52 is linked to the precession axis of the gyro to be rocked thereby. In case of turns to the left or right, the lever 52 will assume one of jthe positions shown in dotted lines, as the case may be, and by means of a connecting rod 53 turn the knob 63, as the 52' is so dimensioned that it will provide suilicient angular motion to shut the ports 31 completely for a turn of appreciable magnitude.

Only one form of an automatic connectionbetween the turn indicator and shut-off ports is shown in Fig.' 5. It is understood, however, that.

other means to accomplish the same purpose could be employed. It is also obvious that knob 40 can be manually operated in case no turn indicator is available.

As many changes could be made in the above construction and many apparently widely diiferent embodiments of this invention could be made without departing from the scope thereof,

it is intended that all matter contained in theA above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described 'my invention. what I claim and desire to secure by Letters Patent is:

1. In an artificial horizon, a universally suspended, self-erecting gyrosoope mounted insubstantially neutral equilibrium having acasing, a" universally suspended pendulum mounted on said 4 casing, a reference member carried by said penv dulum, damping means between .said pendulum and said casing, 'and meansfor locking said pendulum to the gyroscope during turns.

In an artincial horizon, `a gyroscope sus-4 pended for `oscillation .about two axes perpendicular to eachother and mounted in substantial equilibrium, said gyr'oscope having a vertical spin axis and a casing having `a recess forming part of a hollow sphere, means for automatically erecting said spin axis, `a pendulum universally` suspendedfor oscillation about said two axes on said casing, said pendulum having a body .formt .ing part -of a sphere concentric with said irstl named sphere, and .a viscous substancefilling part ofthe gap between said nrst and said last named sphere.

3. In an artiiicial horizon for moving'vehicles, a universally suspended gyroscope mounted 'in substantially neutral equilibrium. having a rotor. l

a casing for said rotor, and'means for erecting said lrotor and casing, a universally suspended damped pendulum on said casing, means to render inactive said erecting means during a turn ci said vehicle, and means to simultaneously arrest Said. pendulum.

- weight adapted to'be raised Atoloclx said pendulum -substantially neutral equilibrium. having 'a rotor,

a'casing for said rotor, and means for erecting said rotor and casing, a universally suspended 5 damped pendulum onsaid casing, means. to ren# y der said erectingmeans inactive during a turn -oi said vehicle. means to simultaneouslyarrest` said pendulum, and means for compensating for. the shift in the center of gravity of the gyroscope due to arresting said-pendulum to maintain the gyro- `scope in neutral equilibrium. -f i 5. In -an artiiicial horizon, aeuniversally suspended pendulum having `a body forming Part 0f a sphere, a casing forming, part of a "hollow 5 sphere, said pendulum being mounted on said casing to maintain said-first named sphere concentric to said last named sphere, a viscous damping mediumj partly nlling the space between said two spheres,`and syroscopic means associe 20k ."erecting means mounted on said casing, a' universally suspended pendulum mounted on said casing, air operated means comprising bellows and a to said'cas'ing, an air inlet for said spinning jets,a second air inlet common to said erecting means and to said bellows, and means to close said last namedfinletduring turns.

4'I .fIn' -an artificial horizon, a universally sus- 35 pended long period pendulum, an. enclosure therefor -also universally mounted, damping vmeans interposed'between said pendulum and said enclosure, an air 'driven vertical gyroscope alsoenclosed in said enclosure, gravity controlled. normally active, air operated'erecting means'for said gyroscope, normally inactive 'air 4operated 4 means to .lock said pendulum in neutral position to said enclosure, and means torender said erect' ing means inactive when the pendulum is locked.45 8. VA11-"artificial horizon as claimed in claim 7,- having kmeans for preventing the locking of said pendulum from disturbing -the neutral equilibium of said universally mounted enclosure.

mslm 11".' 

